I am trying to compare the coral compositions between 2 seasons in 17 sites using PERMANOVA in PRIMER-e v7. I obtained valid results for 16 sites, but it always turned out "negative" for this site (Sharp Island North) every time I ran the test. I have checked that there is no invalid or missing data for the site.
Why is this so? And what can be done to fix it?
Thank you very much in advance!